Urine Sampling

suprapubic aspiration of urine is the first line investigation of infants strongly suspected of having a urinary tract infection and/or requiring antibiotics
bag urine collection is only useful for exclusion of infection if there is no growth of organisms
urine may also be collected via urethral catheter, although (particularly in males), this should only be performed by an experienced clinician

the indications for SPA include
- urine sampling
- relief of obstruction (rarely) - a suprapubic catheter is a better option in this setting
the equipment required includes
- 2 ml or 5ml syringe
- 25g or 23g needle
- skin preparation
- sterile specimen container
- assistant to stop baby moving/extending legs
- consider use of ultrasound to guide attempt (particularly if failed already)
residents not familiar with this procedure should consult a more senior clinician, if possible
consider infant's need for pain relief including possible use of
- application of EMLA (0.5 -1g) to proposed site 60-90 minutes before procedure
- use of oral sucrose (link to section)
- subcutaneous infiltration of lignocaine

the procedure is as follows
- wash hands
- no touch technique
- prepare skin, allow to dry
- attach needle to syringe
- insertion site is 1 cm above symphysis pubis, strictly in midline
- aim is at 90 deg to skin - straight in (bladder is an abdominal organ in infants)
- advance with gentle suction, stopping when urine is obtained
- decant into suitable container
- if unsuccessful, alter angle by about 10 deg and advance again, keeping in midline
  If no urine is obtained after two adjustments of aim, it is likely that bladder is empty. Wait 45-60 minutes and try again.
Interpretation of results
- any leucocytes cells detected on SPA are regarded as abnormal
- any growth in an SPA is theoretically abnormal unless it is clearly a contaminant (e.g. Staph. epidermidis or heavy mixed growth of faecal bacteria)
- there is no limit to the red cell count due to the difficulty in distinguishing traumatic bleeding from true haematuria

the indications for a bag urine include
- failed SPA
- low index of suspicion of urinary tract infection (UTI)
- infant not requiring antibiotics
- collection of urine for purposes other than exclusion of bacterial infection (e.g. analysis of specific gravity, glucose, protein etc)
preparation includes
- area to which bag is applied requires washing with soap and sterile water, rinsing with sterile water and drying
- the bag must be applied with a no touch technique (using sterile gloves)
results are only useful for exclusion of infection if
- no growth
- results are not useful if
  - pure growth
  - mixed growth of >= 100,000 bacteria
  - infants already on antibiotics
a UTI should never be diagnosed or treated on the basis of a bag urine alone
microscopy on bag urine is not warranted, a dip-slide (urinalysis) is more useful

in a very ill infant, strongly suspected of having a UTI and requiring immediate antibiotics:
- take SPA specimen
- if SPA fails, commence antibiotics
- collect SPA as soon as possible
- bag urine specimen useless
in an infant strongly suspected of having a UTI and requiring antibiotics, but not immediately
- take SPA specimen
- if SPA fails, repeat after one hour
- consider use of ultrasound to aid sample collection
- defer antibiotic therapy until SPA obtained, but do not await result
- bag urine specimen useless
in an infant with an illness that might be a UTI but not immediately requiring treatment:
- take SPA specimen
- if SPA fails, order bag urine specimen
- if bag urine specimen result equivocal, take SPA specimen and await result
- if bag urine specimen strongly suggests UTI, take SPA specimen and commence antibiotics
- adjust therapy when SPA result known

Updated 24/06/2009

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